1. Field of the Invention
The present invention relates to a microwave waveguide feed network which has one port typically made of circular or square waveguide used to interface with an antenna, and additional ports for connection to one or more transmitters and/or receivers. More particularly, the present application relates to such microwave feed networks for use in satellite communications.
2. Background
A conventional feed network to transfer a microwave signal between an antenna and a transmitter and receiver is an ortho-mode transducer (xe2x80x9cOMTxe2x80x9d). The OMT is a three-port device, as shown in FIGS. 1A and 1B, which has a circular waveguide port 100 for interfacing with an antenna and two rectangular waveguide ports 102 and 104, each for connecting to a transmitter and/or a receiver. The OMT is often used to feed orthogonal polarizations at ports 102 and 104 to and from the port 100 connected to an antenna used in satellite communications. The two orthogonal polarizations provided at ports 102 and 104 may cover the same or different frequencies.
As the demand for wireless communications increases, the transmission and receiving capacity of communication systems must also increase. Signals provided from a antenna must be provided to more than two ports, with each port potentially having different polarization requirements or different frequency ranges. In order to increase the capacity of a conventional OMT, network elements such as filters, switches and couplers have to be connected to rectangular waveguide ports of the OMT to distribute a signal between the circular waveguide antenna port to additional waveguide ports.
The present invention provides a network with increased channel capacity over an OMT. The network in accordance with the present invention enables a system""s capacity to be upgraded without the need for additional filters, switches or couplers needed to increase the number of ports available on a conventional OMT.
The multi-channel network in accordance with present invention further provides for transferring a signal between a waveguide connected to an antenna and additional ports with a variety of polarizations. For instance, the network can support linear, right hand or left hand circular, dual linear, or dual circular polarizations.
The multi-channel network in accordance with the present invention is further capable of being manufactured using low cost die casting.
The multi-channel network in accordance with the present invention includes a main waveguide section (either square or circular) for propagation of two orthogonal polarizations, an on-axis low pass section which has the same cross section as the main waveguide section, and a high pass section connected perpendicular to the main waveguide section. The low pass section includes a band reject filter (BRF) which is a modified version of a filter described in U.S. Pat. No. 5,739,734. Isolation between the low and high frequency waveguide channel sections is obtained by the rejection performance of the filters, including the BRF and the high pass waveguide section which functions as a filter. Limited disturbance to the cross polarized signals provided from the BRF occurs due to the geometric symmetry of the feed network.
The feed network can be configured to support a number of different polarizations. The feed network can provide two orthogonal linear polarizations for both high and low frequency bands. Orthogonal linear polarizations are provided for the high frequency bands by adding additional high pass sections connected by power dividers, while orthogonal linear polarizations are provided for low frequency bands by adding a conventional OMT. Adding a polarizer between the antenna and main waveguide section enables both the high pass and low pass sections to support left or right hand circular polarization. By adding a 90xc2x0 degree hybrid coupler, the high pass section can support circular polarization alone. By adding a polarizer and OMT after the low pass section, the low pass section can support circular polarization. By using two 90xc2x0 degree hybrid couplers and two power dividers, a network can be created to support dual circular polarization, or dual linear polarization.